Method and device for prevention of adhesion of dirt and contamination on optical parts in laser beam machine

ABSTRACT

In a laser machining system, gas is injected while air is inducted from the rear of a plurality of injection nozzles ( 9   c ) disposed in the space between the machining head ( 3 ) and the workpiece (M) and disposed at stipulated intervals in the direction in which the laser light passes, so as not to disturb the machining gas, thus preventing the adhesion of dust arising during laser machining to optical components ( 31, 32 ) within the head ( 3 ). A light receptor ( 4 ) that receives light reflected or dispersed due to adhered contamination is disposed upstream of the optical components ( 31, 32 ) within the head ( 3 ), and a determination part ( 6 ) compares the light reception value against a preset threshold value.

TECHNICAL FIELD

The present invention relates to a method and apparatus for preventingfouling of optical components in order to prevent deterioration ofmachining quality in a laser machining system.

BACKGROUND

Conventionally, laser machining systems are used for the cutting,drilling, surface machining and marking of steel, nonferrous materials,ceramics, glass, plastic, leather, cloth, wood or various othermaterials (hereinafter referred to as the “workpiece”) as well as forthe welding of steel, nonferrous and other materials (hereinaftercollectively referred to as “machining”). Furthermore, the mainstreamtypes of lasers used include YAG lasers, CO₂ lasers and excimer lasers.

For example, a YAG laser machining system may have a constitutionwherein laser light generated by a laser oscillator is transmittedthrough an optical fiber, and concentrated onto the workpiece by meansof a condensing lens provided within the head. Moreover, such a head canbe manipulated in three dimensions according to an operating procedurestored in a computer or the like, thus permitting extremely finemachining to be performed. Note that protective glass that protects thecondensing lens from spatter, fumes, dust and the like (hereinafterreferred to as simply “dust”) arising during the machining of theworkpiece is provided in the space between the condensing lens and theworkpiece. In addition, shield gases, assist gases and other processgases (hereinafter referred to as simply “process gases”) are suppliedto the machining area, thus preventing deterioration of the machiningquality.

However, in the laser machining as described above, dust arising duringmachining may adhere to the protective glass and the like, thuspreventing the condensing of laser light and causing deterioration inmachining quality. To solve this problem, the publication of unexaminedJapanese patent application (Kokai) No. JP-A H11-239889 proposes aconstitution that comprises a nozzle through which laser light (referredto as a “laser beam” in the publication) and process gases may pass. Theconstitution further comprises a plurality of ring-shapedflow-straightening plates provided in front of the condensing lensinside a nozzle holding space such that their inside diameter becomessmaller the closer they are to the workpiece. Gases injected from thegas injection nozzle along the flow-straightening plates can beexhausted from internal spaces in the nozzle holder to external spaces.By adopting such a constitution, it is possible to completely block dustduring machining and protect the condensing lens, and thus preventfouling of the window.

In addition, JP-A H05-256947 proposes an internal contaminationdetection technique for distance measuring apparatus based on opticalmeans. This technique is one whereby fouling of the lens or front glassor the like is detected by catching part of the light used for measuringdistances which is scattered backward at the time that the light passesthrough the lens or front glass or the like.

However, the apparatus proposed in JP-A H11-239889 does not take intoconsideration the suction of air from the side opposite the gasinjection nozzle. Accordingly, when the amount of gas ejected from thegas injection nozzle becomes large, then negative pressure is generatedin the vicinity of the gas ejection nozzle, thus drawing in dust in thevicinity and giving rise to turbulent flow also in the interior of theholder, so the ability to exhaust dust is decreased and the ability toprevent the adhesion of dust is also decreased. In addition, while aplurality of ring-shaped flow-straightening plates is provided in orderto straighten the flow of gas ejected from the gas injection nozzle andblock dust, if the amount of gas ejected from the gas injection nozzlebecomes large, then the atmospheric gas in the machining area will alsobe simultaneously drawn in. Accordingly, the normal machining atmospherecannot be maintained and the meritorious effect of theflow-straightening plates is diminished and machining qualitydeteriorates.

In addition, the apparatus proposed in JP-A H05-256947 uses a specialoptical lens in order to catch the light scattered by fouling, so thehead becomes large, thereby adding limitations to the machiningorientations and otherwise reducing its degrees of freedom. In addition,in the case that this technique is adopted in a laser machining system,the machining laser is high-powered in contrast to one used formeasuring distances, so quartz glass is used for the condensing lens andthe fabrication of a special lens using this quartz glass is difficult.Moreover, while the measurement of distance is performed by catchingreflected light from the light given off, the intensity of light fromoutside the apparatus is also caught at the same time. Accordingly,regardless of any fouling of the lens, front glass or the like, theintensity of light caught may also vary depending on the season,weather, time of day or other circumstances at the time of measurement,thereby giving rise to dispersion in the detection data and poorreliability.

The present invention came about in order to solve the aforementionedproblems and has as its object to provide a method and apparatus forpreventing the fouling of optical components by the adhesion of dustarising during laser machining, by inducting air from the rear of theinjection area while injecting gas in the direction in which the laserlight passes, so as not to disturb the machining gas, in the spacebetween the workpiece and the head that concentrates laser light fromthe light source and irradiates the workpiece.

BRIEF SUMMARY

The present invention prevents the dust arising during laser machiningfrom adhering to optical components by: in the space between a workpieceand optical components that condense laser light from a light source andshine it on the workpiece, injecting gas while inducting air from therear of a plurality of injectors disposed at stipulated intervalsbetween them in the direction in which the laser light passes, so as notto disturb the machining gas.

The method of the present invention can be implemented by an apparatusaccording to the present invention wherein a plurality of nozzles ableto induct air from behind while injecting gas toward laser lightirradiated toward the workpiece is provided to the side of the spacebetween the optical components and the workpiece.

Moreover, by doing so it is possible to prevent disturbance to themachining gas during laser machining. In addition, no disturbance occursin the flow of air from behind the injectors, and the flow of gas fromthe nozzles is stabilized, thus preventing gas that contains dust frombeing drawn in and allowing clean gas to be blown toward the path inwhich the laser light passes. Even if drifting dust is present, it canbe exhausted immediately out of the system without allowing it to remainlong, so dust and the like that arises during laser machining can beprevented from adhering to the optical components of the head.

Each of the plurality of nozzles smoothes the flow of air inducted frombehind and is preferably given a shape, e.g. a streamlined shape, thatdoes not allow a negative pressure to arise in the vicinity of theinjectors. In addition, it is preferable that the nozzles adjacent tothe workpiece be disposed such that they are close to the centerline ofthe laser light, and the length of the nozzles preferably becomesshorter the closer they are to the workpiece. In addition, among theplurality of nozzles, it is preferable that those closer to theworkpiece be pointed in a direction perpendicular to the direction inwhich the laser light passes, while the nozzles near the head be pointedtoward the workpiece from the direction perpendicular to the directionin which the laser light passes. By doing so, in addition to thefunction of the nozzle alone, the synergistic effect of thisconfiguration is added so that the atmosphere is further from that ofthe dusty atmosphere the closer one gets to the optical components, sodust is no longer present in the path in which the laser light passes.

In addition, the present invention comprises the aforementionedapparatus according to the present invention wherein a plurality offlow-straightening plates are disposed in the space between saidplurality of nozzles and the workpiece, at stipulated intervals betweenthem in the direction in which the laser light passes. Theseflow-straightening plates enhance the aforementioned function andmeritorious effects.

In addition, in the present invention, a radiant heat barrier isdisposed on the workpiece side of the flow-straightening plates. Byplacing a radiant heat barrier in the location that is most susceptibleto the effects of machining heat, the conduction of heat to the opticalcomponents within the head is effectively prevented, so the effect ofpreventing thermal deterioration is well achieved.

In addition, in the present invention, a machining atmospheric gasnozzle is provided upon said radiant heat barrier. This machiningatmospheric gas nozzle can maintain a good machining atmosphere withoutdisturbance, thereby preventing deterioration of the machining quality.

The present invention is also any of the apparatus according to thepresent invention described above, wherein an injection nozzle thatinjects gas toward the gas injected by said plurality of nozzles isdisposed in the vicinity of those optical components closest theworkpiece among the optical components. By means of this injectionnozzle, it is possible to push down the blow-up of dust-containing gasfrom the machining area, the more in the atmosphere closest to theoptical components nearest the workpiece, and thus the prevention offouling of optical components nearest the workpiece can be done evenmore effectively. By injecting gas from this injection nozzle directlyonto the optical components closes the workpiece, then a major effect ofcooling the optical components closes the workpiece can be achieved, sothe adhesion of dust to these optical components can be completelyprevented. Even if dust should adhere, the adhered dust is blown off.The injected gas travels down and combines with the gas from theaforementioned plurality of nozzles, thereby achieving an even bettereffect of preventing dust adhesion.

The present invention is also any of the apparatus according to thepresent invention described above, wherein a suction nozzle is disposedon the side opposite that of said plurality of nozzles such that theylie on either side of the path in which the laser light passes. Thissuction nozzle can suck up dust arising during laser machining.

The present invention is also any of the apparatus according to thepresent invention described above, wherein a pair of side plates thatunidirectionally guide the flow of gas injected from these nozzles isdisposed with one on either side of said plurality of nozzles. Theseside plates assist the function of the aforementioned nozzle.

The present invention is also any of the apparatus according to thepresent invention described above, comprising an apparatus for detectingthe fouling of optical components which comprises: a light receptordisposed on the upstream side of said optical components that transmitsor reflects laser light while also reflecting or transmitting andreceiving reflected light and scattered light arising from foulingadhering to the optical components, and a determination part thataccepts input of said reflected light and scattered light received bysaid light receptor and makes a determination as to whether or not thevalue of this input reflected light and scattered light exceeds athreshold value. This fouling detection apparatus eliminates opticalnoise and permits accurate detection of fouling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a diagram of the constitution of an apparatus forpreventing the fouling of optical components according to the presentinvention, which is installed in a YAG laser machining system, alongwith a partial cross section of the fouling detection apparatus thatconstitutes this fouling prevention apparatus;

FIG. 1(b) is a front view illustrating a partial cross section of afirst embodiment of the apparatus for preventing the fouling of opticalcomponents according to the present invention;

FIG. 2 is a diagram of a second embodiment of the fouling preventionapparatus shown in partial cross-section;

FIG. 3 is a diagram of a third embodiment of the fouling preventionapparatus shown in partial cross-section;

FIG. 4 is an explanatory diagram of a machining atmospheric gas nozzlesuited to welding;

FIG. 5 is an explanatory diagram of a machining atmospheric gas nozzlesuited to cutting;

FIG. 6 is a diagram of a fourth embodiment of the fouling preventionapparatus shown in partial cross-section, where (a) is a front viewthereof and (b) is a side view thereof;

FIG. 7 is a partial cross-sectional constitution diagram of anotherembodiment of the fouling prevention apparatus according to the presentinvention provided with a fouling detection apparatus;

FIG. 8 is a partial cross-sectional constitution diagram of anotherembodiment of the fouling detection apparatus constituting the apparatusfor preventing the fouling of optical components according to thepresent invention; and

FIG. 9 is a diagram illustrating the processing of the determinationpart of the fouling detection apparatus, where (a) illustrates the caseof no fouling present, (b) illustrates the case of fouling present and(c) is a diagram of the case in which a machining defect has occurred.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERREDEMBODIMENTS

In order to describe the present invention in detail, here follows adescription made with reference to the appended FIGS. 1-9.

We shall first describe in detail the apparatus for preventing thefouling of optical components according to the present invention.

In FIG. 1(a), 1 is a laser oscillator that generates laser light, andthe laser light thus generated is transmitted via an optical fiber 2,focused within a head 3 and used to irradiate the workpiece M.

Within the head 3 are provided a condensing lens 31 that concentrateslaser light and a protective glass 32 that protects this condensing lens31 from dust, in this order when going toward the workpiece M. Note that33 is the head frame while 8 indicates a nozzle for supplying shieldgas. The constitution thereof is the same as in the prior art.

The fouling prevention apparatus 9 according to the present invention isdisposed between the head 3 and the workpiece M, and may take the shapeof an inverted truncated cone (the shape of a cone with its top portioncut off and then inverted vertically), for example. Moreover, itscentral portion serves as the path in which the laser light passeswherein light is concentrated by the condensing lens 31 from top tobottom with the focus of the laser light lying upon the workpiece M.

FIG. 1(b) illustrates the first embodiment of the fouling preventionapparatus 9 of the present invention, wherein five nozzles 9 c, forexample, may be attached along the left side (in the plane of the paper)of a frame 9 b at fixed intervals in the vertical direction in the planeof the paper.

The nozzles 9 c have elliptical cross sections that are flattened in thevertical direction in the drawing, in a constitution which provides anumber of circular nozzle holes 9 d, for example, that inject gas towardthe laser light. By making the cross sections of the nozzles 9 celliptical, when gas is injected, the amount of air inducted from therear of the nozzles 9 c is assured and the flow of this air becomes evensmoother. When gas is injected from nozzles 9 c of such a shape, the airin the surroundings that is drawn into the injected gas also assumes thesame flow as the gas, so no negative pressure is generated in thevicinity of the nozzles 9 c.

At this time, in the event that there are no gaps between the nozzles 9c where air in the vicinity can adequately flow, and the shape is one towhich the flow of air does not become accustomed, then negative pressurearises in front of the nozzles 9 c, giving rise to vortices in theinjected gas or inflowing air or causing turbulence, thus agitating theatmosphere in the path in which the laser light passes, so theeffectiveness of the exhausting of drifting dust is decreased.

However, the present invention is constituted such that air to the rearof this nozzles 9 c can be inducted in the flow-straightened state frombetween the nozzles 9 c, so the injected gas and inducted air flowthrough the path, in which the laser light passes, in theflow-straightened state, thus pushing out any dust present andpreventing the adhesion of dust to optical components. Moreover, whenlooking from above in the plane of the paper in FIG. 1(b), these nozzles9 c may be provided with a plurality of nozzle holes 9 d present in along, narrow strip at stipulated intervals apart, for example, so thegas can be ejected in a band shape toward the irradiated laser light.Note that 9 m is a filter that prevents the inducted air from containingdust.

Here, 9 j indicates flow-straightening plates provided toward the sideof the workpiece M from the nozzles 9 c, being provided substantiallyperpendicular to the direction in which the laser light passes, withthree plates disposed equidistantly. These flow-straightening plates 9 jform a boundary that separates the upper and lower atmospheres, so theshield gases used in laser machining are not disturbed by the gasinjected from the nozzles 9 c. In addition, even if dust-containing gasgenerated in the machining area should approach these flow-straighteningplates 9 j, the dust-containing gas will flow horizontally, guided bythe flow-straightening plates 9 j, and the dust will not go toward thehead 3. These flow-straightening plates 9 j exhibit adequateeffectiveness even if only a few are provided at intervals of roughly acouple of mm.

In addition, with this embodiment, the aforementioned nozzles 9 c andflow-straightening plates 9 j are disposed closer to the central axis ofthe laser light the nearer they are to the workpiece M. The path inwhich the laser light passes becomes smaller the closer it gets to theworkpiece M, so in order to protect the optical components from dust andthe heat of working, it is effective for the nozzles 9 c andflow-straightening plates 9 j to be disposed as described above andnarrow their range of effect.

Now, 9 k is a radiant heat barrier disposed further toward the workpieceM side of the flow-straightening plates 9 j so as to secure the path inwhich the laser light passes. This radiant heat barrier 9 k may have aconstitution wherein cooling water within a water channel flows from oneend to the other end, for example. The water channel is preferably madeof a metal with good cooling performance such as copper, for example. Bydisposing this radiant heat barrier 9 k at a position closest to theworkpiece M that is most susceptible to the effects of heat duringmachining, it exhibits a superior cooling effect and is able to greatlyprevent deterioration of the condensing lens 31, protective glass 32 andother optical components within the head 3.

Moreover, in this first embodiment, an injection nozzle 9 n is providedimmediately below the protective glass 32. This injection nozzle 9 n isannular in shape, with the path in which the laser light passes beingformed in its center. The nozzle holes 9 na of the injection nozzle 9 nmay point upward, for example, so that they blow gas directly onto theoutside surface of the protective glass 32. In this manner, even ifdust-containing gas was to float upward and dust was to adhere to theprotective glass 32, it can be adequately removed and there is also theeffect of cooling the protective glass 32. In addition, the blown gaswill drop after coming into contact with the protective glass 32, thuspreventing dust from floating up at this time also.

In this first embodiment, the gas injected from injection nozzle 9 n isblown directly onto the outside surface of the protective glass 32, buteven if the nozzle holes 9 na of this injection nozzle 9 n were to pointdownward, thus joining with the gas injected from the nozzles 9 c, thiscan prevent dust from floating up and prevent the adhesion of dust tothe protective glass 32.

FIG. 2 illustrates the second embodiment of the fouling preventionapparatus 9. In this second embodiment, the filter 9 m is eliminatedfrom the fouling prevention apparatus 9 illustrated in the firstembodiment above, and a suction nozzle 9 o is disposed on the sideopposite that of the nozzles 9 c such that they lie on either side ofthe path in which the laser light passes.

In this second embodiment, this suction nozzle 9 o sucks up any dustgenerated during laser machining. Even though the suction flow of thissuction nozzle 9 o may be greater than the gas flow ejected from theplurality of nozzles 9 c, the plurality of nozzles 9 c induct air sothis is no problem. In addition, even if the plurality of nozzles 9 cshould fail, a certain degree of function can be maintained by means ofthis suction nozzle 9 o.

In addition, FIG. 3 illustrates the third embodiment of the foulingprevention apparatus 9. In this third embodiment, the suction nozzle 9 ois eliminated from the fouling prevention apparatus 9 illustrated in thesecond embodiment above, and a machining atmosphere gas nozzle 9 p isprovided in the radiant heat barrier 9 k.

By providing this machining atmosphere gas nozzle 9 p, a good machiningatmosphere can be maintained without disturbance, so it is possible toprevent deterioration of the machining quality. When used for welding,for example, as shown in FIG. 4, this machining atmosphere gas nozzle 9p preferably has a double gas jacket 9 pa in the portion near the laserand a single gas jacket in the lower portion on the side of theworkpiece M. When used for cutting, as shown in FIG. 5, a sharp-tippeddouble or triple gas jacket 9 pa is preferable. When vapor-depositedmetal or a metal mesh 9 paa is deposited on the interior of this gasjacket 9 pa (on the side of the workpiece M within the double gas jacket9 pa illustrated in FIG. 4), it is possible to prevent damage due tolaser light reflected from the workpiece M, and this also has aflow-straightening effect.

FIG. 6 illustrates the fourth embodiment of the fouling preventionapparatus 9. In this embodiment, a top frame 9 a for connecting to thehead 3 is provided on the top edge of the fouling prevention apparatus9, and a pair of side plates 9 e (equivalent to the frame 9 b) thatmaintain the path in which the laser light passes is attached to thistop frame 9 a. Moreover, five nozzles 9 c with circular cross sectionsare attached to the side edges of this pair of side plates 9 e (to theleft in the plane of the paper in FIG. 6(a)) such that a constantinterval is maintained in the up and down direction in the plane of thepaper.

In the case of fouling prevention apparatus 9 of the same size (height),if the cross-sectional shape of the nozzles 9 c is made circular as isadopted in the fourth embodiment, then the gaps between adjacent nozzles9 c become smaller, the amount of air inducted by the gaps betweennozzles 9 c may become inadequate, and a negative pressure may arise inthe vicinity of the nozzles due to this inadequate amount of air.Accordingly, in this fourth embodiment, notches 9 h are provided on thenozzle 9 c side of the side plates 9 e, thus increasing the amount ofair inducted from the gaps between the nozzles 9 c. Thereby, turbulencedoes not occur in the inducted air, preventing dust-containing gas frombeing drawn into the path in which the laser light passes, and thusachieving the effect of exhausting dust when dust is present. Moreover,the pair of side plates 9 e further isolate the path in which the laserlight passes from the effects of the surrounding, thus blocking theintrusion of dust-containing gas and forming a unidirectional gas flowin the direction from the nozzles 9 c.

In addition, slit-shaped nozzle holes 9 d are provided on the nozzles 9c in the direction in which the laser light passes (the direction ofpenetrating the pair of side plates 9 e; see FIG. 6(b)). In thisembodiment 4, among the five nozzles 9 c, the lower three inject gas ina direction substantially perpendicular to the direction in which thelaser light passes, while the upper two inject gas toward the workpieceat an angle of 10-20° toward the direction perpendicular to thedirection in which the laser light passes (see FIG. 6(a)). This preventsdust-containing gas from being blown up into the atmosphere near theprotective glass 32.

Furthermore as shown in FIG. 6(b), in this fourth embodiment, the lengthof the long, thin nozzles 9 c becomes shorter the closer they are to theworkpiece M. This is so that they match the shape of the path in whichthe laser light passes, thus avoiding the use of unnecessary gas to beinjected and making the fouling prevention apparatus 9 more compact andlightweight. In particular, when the side plate 9 e are provided as inthe fourth embodiment, the function and meritorious effects of theseside plates 9 e are compounded, so it is possible to adequately preventdust-containing gas from being blown in even if the nozzles 9 c adjacentto the workpiece M are shortened.

Note that each of the nozzles 9 c, which are omitted from the drawing,is individually connected to the opposite side of the nozzle holes 9 dby a distribution line used to distribute the gas to be injected.

In the fouling prevention apparatus 9 according to the presentinvention, it is preferable for the pressure of gas injected from thenozzles 9 c to become greater the closer to the workpiece M, thusadequately shielding from dust-containing gas in areas near theworkpiece M. In order to achieve this, the gas supply from theindividual supply lines to the distribution lines should preferably beperformed from the side closer to the workpiece M, thus increasing thegas pressure within the distribution lines near the workpiece M andincreasing the supply pressure to the nozzles 9 c near the workpiece M.

It is preferable that the volume within the nozzles 9 c be increased toform reservoirs 9 g and for the gas injection volume (pressure) to bemade equal at each portion of the nozzle holes 9 d. The area in front ofthe nozzle holes 9 d is a cavity which is the path in which the laserlight passes, so the reaction force of injected gas borne by the nozzleholes 9 d is small. Accordingly, the pressure within the nozzles 9 c isapt to decrease and the meritorious effect of providing the reservoirs 9g is great. For this reason, it is preferable for the nozzles 9 c to betubular. In the fourth embodiment, the nozzles 9 c are cylindrical. Inthe event that no reservoirs 9 g are provided, the pressure would begreatest at the gas introduction position for the nozzles 9 c, with thepressure decreasing the further away from the gas introduction position,so the gas exhaust pressure is different depending on the position ofthe nozzle holes 9 d.

Note that regarding the providing of flow-straightening plates 9 j andthe radiant heat barrier 9 k, and regarding the providing of theinjection nozzle 9 n, this is the same in the fourth embodiment as inthe first-third embodiments, so an explanation is omitted.

The apparatus for preventing fouling of optical components in a lasermachining system according to the present invention is as describedabove, but:

-   {circle over (1)} providing a filter in the injected gas supply    route in order to purify the injection gas,-   {circle over (2)} adopting air for the injected gas,-   {circle over (3)} providing a valve that can adjust the flow rate on    the upstream side of the nozzles 9 c,-   {circle over (4)} adopting a constitution wherein the installation    intervals between the nozzles 9 c and flow-straightening plates 9 j    can be changed or adjusted, and-   {circle over (5)} adopting a constitution wherein the width of the    openings of the nozzle holes 9 d can be changed or adjusted    depending on the position of the nozzles 9 c,-   and the like are each included within the technical scope of the    present invention.

Note that the phantom-line arrows (double-dashes line) in FIG. 1(b),FIGS. 2-3 and FIG. 6(a) represent the flow of gas discharged from thenozzle holes 9 d. In addition, the method of transmitting the laserlight from the laser oscillator 1 to the head 3 is not limited to theoptical fiber 2, but rather it may also be conducted by means of areflective mirror 10 as shown in FIG. 7. In addition, these embodimentswere described using the head of a YAG laser machining system as anexample, but the present invention is in no way limited to the head of aYAG laser machining system but rather it is applicable to the head ofany type of laser machining system.

Here follows a description of a fouling detection apparatus which is aconstituent element of the apparatus for preventing fouling of opticalcomponents in a laser machining system according to the presentinvention, made with reference to the embodiments illustrated in FIG.1(a) and FIGS. 7-9.

In the diagram of the constitution of the partial cross section of theYAG laser machining system of FIG. 1(a), it was previously describedthat the condensing lens 31 and protective glass 32 are provided withinthe head 3.

This head 3 is susceptible to being directly exposed to dust-containinggas arising at the time of machining of the workpiece M, so measures toprevent the adhesion of dust to the head 3 have been tried, but thereare cases in which dust adheres to the condensing lens 31, protectiveglass 32 and other optical components not only due to long-term usagebut also due to merely being stored for a long time depending on thestorage location.

When dust is adhering to the condensing lens 31 and protective glass 32,diffuse reflection occurs due to this dust when the laser light receivedby the head 3 passes through. In addition, the index of refraction oflaser light also changes and the machining precision of the workpiece Mdeteriorates. Accordingly, close attention must be paid to the foulingof optical components, and it is occasionally necessary to detect thepresence of fouling.

The apparatus for preventing fouling of optical components 9 accordingto the present invention provided with a fouling detection apparatus hasa constitution such that a light receptor 4 is provided upstream of thecondensing lens 31, and the reflected light and scattered light arisingfrom fouling adhering to the condensing lens 31 and protective glass 32is received by the light receptor 4.

For example, in the examples of FIG. 1(a) and FIG. 7, a laserlight-transmitting/reflecting mirror 34 is provided on the upstream sideof the condensing lens 31, so that laser light irradiated through theceiling area of the head frame 33 is transmitted and reaches thecondensing lens 31 and protective glass 32. On the other hand, lightscattered from the condensing lens 31 and protective glass 32 due tofouling is reflected by the laser light-transmitting/reflecting mirror34 and received by the light receptor 4 provided on the side of the headframe 33.

In addition, in the example of FIG. 8, a laserlight-reflecting/transmitting mirror 35 is provided on the upstream sideof the condensing lens 31, and the laser light irradiated from the sideof the head frame 33 is reflected by this laserlight-reflecting/transmitting mirror 35 toward the condensing lens 31and protective glass 32. On the other hand, scattered light andreflected light from the condensing lens 31 and protective glass 32 dueto fouling is transmitted through the laserlight-reflecting/transmission mirror 35 and received by the lightreceptor 4 provided on the ceiling of the head frame 33.

The light receptor 4 receives the reflected light and scattered lightand converts the intensity of this received light into an intensitysignal. The intensity of the signal increases as the amount of dustadhering becomes greater. The signal value from the light receptor 4 isconducted to the determination part 6 by a transmission cable 5.

The determination part 6 takes the transmitted signal value to be thereceived-light value and determines whether or not fouling is present bycomparing the received-light value against a preset threshold value.

FIG. 9 is a plot illustrating the received-light value at the lightreceptor 4 in the case in which fouling is present and the case in whichno fouling is present, with the intensity of the received-light value atthe light receptor 4 due to laser-light irradiation presented on thevertical axis, at various times from the start of laser irradiation tothe end of irradiation on the horizontal axis.

In the example of this FIG. 9, in the case of (a) where the protectiveglass 32 and condensing lens 31 are not fouled, the received-light valuefluctuates between the values P_(max) and P_(min). On the other hand,when the protective glass 32 and condensing lens 31 are fouled, thereceived-light value fluctuates at values much higher than P_(max) asshown in (b).

Accordingly, by setting this value of P_(max) as the threshold value, itis easy for the determination part 6 to detect whether or not theprotective glass 32 and condensing lens 31 are fouled. Note that when amachining defect occurs, the threshold value P_(min) will also beexceeded, but as shown in (c), the amplitude of fluctuation will begreater than in the case of fouling, so it is easy to distinguish thisfrom the case of fouling.

In the event that fouling is detected based on the determination of thedetermination part 6, the results thereof may be sent to a displaydevice or sent to an alarm device 7, thus attracting the notice of theworker.

When fouling is investigated using this fouling detection apparatus, itis preferably performed in the state in which no laser machining isactually performed and no problems would occur if the laser light isirradiated for detection, where laser light is irradiated in a locationwhere there is little reflected light other than from the head, and thenthe light reflected and scattered from the condensing lens 31 andprotective glass 32 due to the incident laser light is caught toincrease the detection accuracy. When detection is performed whileperforming laser machining, the light reflected from the machining areais also caught by the light receptor at the same time, so there is arisk of a false positive indication of fouling present depending on thetype of machining, so in this case, it is necessary to set the thresholdvalue in consideration of light reflected from the machining area. Notethat the mounting location of the light receptor 4 differs between theexample of FIGS. 1(a) and 7 and the example of FIG. 8, so the thresholdvalue should also be set separately in these cases.

INDUSTRIAL USABILITY

As described above, the present invention is able to effectively preventdust arising during machining from adhering to the condensing lens andprotective glass. In addition, if a fouling detection apparatus isprovided, superior detection can be performed reliably without givingrise to dispersion in the detection data depending on the situation atthe time of detection.

1. A method for preventing the fouling of optical components in a lasermachining system comprising the steps of: in a space between a workpieceand optical components that condense laser light from a light source andirradiate it on the workpiece, injecting gas while inducting air fromthe rear of a plurality of injectors disposed at stipulated intervals ina direction in which the laser light passes, so as not to disturb themachining gas, thereby preventing fumes, spatter and dust arising duringlaser machining from adhering to said optical components.
 2. Anapparatus that performs the fouling prevention method according to claim1, comprising: a plurality of nozzles that inject gas toward the laserlight irradiated toward the workpiece while inducting air from behind,the plurality of nozzles being provided along a side of a space betweenthe optical components and the workpiece.
 3. An apparatus for preventingthe fouling of optical components in a laser machining system accordingto claim 2, wherein a plurality of flow-straightening plates is disposedbetween said plurality of nozzles and the workpiece, at stipulatedintervals in the direction in which the laser light passes.
 4. Anapparatus for preventing the fouling of optical components in a lasermachining system according to claim 3, wherein a radiant heat barrier isdisposed on the workpiece side of the flow-straightening plates.
 5. Anapparatus for preventing the fouling of optical components in a lasermachining system according to claim 4, wherein a machining atmosphericgas nozzle is provided upon said radiant heat barrier.
 6. An apparatusfor preventing the fouling of optical components in a laser machiningsystem according to any of claims 2-5, wherein an injection nozzle thatinjects gas toward the gas injected by said plurality of nozzles isdisposed in the vicinity of optical components closest the workpieceamong the optical components.
 7. An apparatus for preventing the foulingof optical components in a laser machining system according to any ofclaims 2-5, wherein a suction nozzle is disposed on the side oppositethat of said plurality of nozzles with respect to the path in which thelaser light passes.
 8. An apparatus for preventing the fouling ofoptical components in a laser machining system according to claim 6,wherein a suction nozzle is disposed on the side opposite that of saidplurality of nozzles with respect to the path in which the laser lightpasses.
 9. An apparatus for preventing the fouling of optical componentsin a laser machining system according to any of claims 2-5, wherein apair of side plates that unidirectionally guide the flow of gas injectedfrom these nozzles is disposed with one on either side of said pluralityof nozzles.
 10. An apparatus for preventing the fouling of opticalcomponents in a laser machining system according to claim 6, wherein apair of side plates that unidirectionally guide the flow of gas injectedfrom these nozzles is disposed with one on either side of said pluralityof nozzles.
 11. An apparatus for preventing the fouling of opticalcomponents in a laser machining system according to claim 7, wherein apair of side plates that unidirectionally guide the flow of gas injectedfrom these nozzles is disposed with one on either side of said pluralityof nozzles.
 12. An apparatus for preventing the fouling of opticalcomponents in a laser machining system according to claim 8, wherein apair of side plates that unidirectionally guide the flow of gas injectedfrom these nozzles is disposed with one on either side of said pluralityof nozzles.
 13. An apparatus for preventing the fouling of opticalcomponents in a laser machining system according to any of claims 2-5,comprising an apparatus for detecting the fouling of optical componentswhich comprises: a light receptor disposed on the upstream side of saidoptical components that transmits or reflects laser light while alsoreflecting or transmitting and receiving reflected light and scatteredlight arising from fouling adhering to the optical components, and adetermination part that accepts input of said reflected light andscattered light received by said light receptor and makes adetermination as to whether or not the value of this input reflectedlight and scattered light exceeds a threshold value.
 14. An apparatusfor preventing the fouling of optical components in a laser machiningsystem according to claim 6, comprising an apparatus for detecting thefouling of optical components which comprises: a light receptor disposedon the upstream side of said optical components that transmits orreflects laser light while also reflecting or transmitting and receivingreflected light and scattered light arising from fouling adhering to theoptical components, and a determination part that accepts input of saidreflected light and scattered light received by said light receptor andmakes a determination as to whether or not the value of this inputreflected light and scattered light exceeds a threshold value.
 15. Anapparatus for preventing the fouling of optical components in a lasermachining system according to claim 7, comprising an apparatus fordetecting the fouling of optical components which comprises: a lightreceptor disposed on the upstream side of said optical components thattransmits or reflects laser light while also reflecting or transmittingand receiving reflected light and scattered light arising from foulingadhering to the optical components, and a determination part thataccepts input of said reflected light and scattered light received bysaid light receptor and makes a determination as to whether or not thevalue of this input reflected light and scattered light exceeds athreshold value.
 16. An apparatus for preventing the fouling of opticalcomponents in a laser machining system according to claim 8, comprisingan apparatus for detecting the fouling of optical components whichcomprises: a light receptor disposed on the upstream side of saidoptical components that transmits or reflects laser light while alsoreflecting or transmitting and receiving reflected light and scatteredlight arising from fouling adhering to the optical components, and adetermination part that accepts input of said reflected light andscattered light received by said light receptor and makes adetermination as to whether or not the value of this input reflectedlight and scattered light exceeds a threshold value.
 17. An apparatusfor preventing the fouling of optical components in a laser machiningsystem according to claim 9, comprising an apparatus for detecting thefouling of optical components which comprises: a light receptor disposedon the upstream side of said optical components that transmits orreflects laser light while also reflecting or transmitting and receivingreflected light and scattered light arising from fouling adhering to theoptical components, and a determination part that accepts input of saidreflected light and scattered light received by said light receptor andmakes a determination as to whether or not the value of this inputreflected light and scattered light exceeds a threshold value.
 18. Anapparatus for preventing the fouling of optical components in a lasermachining system according to claim 10, comprising an apparatus fordetecting the fouling of optical components which comprises: a lightreceptor disposed on the upstream side of said optical components thattransmits or reflects laser light while also reflecting or transmittingand receiving reflected light and scattered light arising from foulingadhering to the optical components, and a determination part thataccepts input of said reflected light and scattered light received bysaid light receptor and makes a determination as to whether or not thevalue of this input reflected light and scattered light exceeds athreshold value.
 19. An apparatus for preventing the fouling of opticalcomponents in a laser machining system according to claim 11, comprisingan apparatus for detecting the fouling of optical components whichcomprises: a light receptor disposed on the upstream side of saidoptical components that transmits or reflects laser light while alsoreflecting or transmitting and receiving reflected light and scatteredlight arising from fouling adhering to the optical components, and adetermination part that accepts input of said reflected light andscattered light received by said light receptor and makes adetermination as to whether or not the value of this input reflectedlight and scattered light exceeds a threshold value.
 20. An apparatusfor preventing the fouling of optical components in a laser machiningsystem according to claim 12, comprising an apparatus for detecting thefouling of optical components which comprises: a light receptor disposedon the upstream side of said optical components that transmits orreflects laser light while also reflecting or transmitting and receivingreflected light and scattered light arising from fouling adhering to theoptical components, and a determination part that accepts input of saidreflected light and scattered light received by said light receptor andmakes a determination as to whether or not the value of this inputreflected light and scattered light exceeds a threshold value.